1. Technical Field
One or more of the embodiments of the present invention relate to an emission control system for removal of regulated combustion components from the exhaust of a combustion process, such as an internal combustion engine.
2. Background Art
Exhaust from a combustion engine typically contains a variety of combustion components or gases such as unburned hydrocarbon (HC), carbon monoxide (CO), particulate matter (PM), nitric oxide (NO), and nitrogen dioxide (NO2), with NO and NO2, collectively referred to as nitrogen oxide or NOx.
Conventional emission control systems often use separate devices for the reduction of NOx or particulate matter. For example, in one conventional such system, a singular SCR (selective catalytic reduction) catalyst is used for converting NOx to nitrogen (N2) and a singular particulate filter (PF) is used for removing particulate matter. In this situation, the singular SCR catalyst and the singular particulate filter can be sequentially aligned and disposed separable from each other.
In at least situations where space conservation may be a consideration, a combined singular SCR catalyst on a particulate filter unit (SCR/PF) has been explored. In these instances, the pore size of the particulate filter is generally increased and the SCR washcoat is applied onto the filter and into the pores. One problem that has been observed with SCR/PFs is that the backpressure of the filter unit significantly increases as a result of the SCR material disposed in the filter pores. Also, since the SCR/PF is wall-flow technology, the gas passes through the SCR/PF in a non-uniform manner, with the majority of the gas typically flowing through axial center of the filter substrate. This contributes to the high pressure drop observed with SCR/PF use (since much of the gas is going through a relatively small portion of the filter) and decreases the overall effectiveness of the SCR for NOx reduction (since a relatively small percentage of the SCR material is being exposed to the exhaust gas).
There is thus a continuing need to provide an emission control system with a relatively small space consumption and/or a relatively high NOx reduction efficiency while minimizing system complexity.